Friction welder

ABSTRACT

An apparatus for friction welding a first element to a second element includes a forge assembly having a table defining a platform, a crank, a forge link and a reaction link disposed oppositely of the forge link relative to the platform. Various construction details are disclosed that provide a friction welder that minimizes bending in the forge and motion planes and enhances repeatability of the welds performed. In a specific embodiment, the friction welder may be used in a method to form integrally bladed rotors and further includes a reciprocal motion assembly adapted to generate motion between the elements being welded, a gripper and an base tool. The reciprocal motion assembly includes a servo hydraulic actuator having a hydraulic column frequency greater than the frequency of reciprocation. The gripper is a device for use with bonding an airfoil to the rotor. The base tool is a device for mounting and positioning the rotor for the bonding operations.

CROSS-REFERENCE

The present application is related to the subject matter disclosed inU.S. patent application Ser. No. 09/187,511 filed Nov. 6, 1998 now U.S.Pat. No. 6,244,495 filed on the same date as this application, entitled“Gripper”, as well as the subject matter disclosed in the U.S. patentapplication Ser. No. 09/187,073 filed Nov. 6, 1998, now abandoned alsofiled on the same date as this application, entitled “Indexing Turret.”Both of these applications are incorporated herein by reference in theirentirety.

TECHNICAL FIELD

This invention relates to friction welders, and more particularly toservo hydraulically driven friction welders.

Although the invention was developed in the field of aircraft engines ithas application to other fields where friction welding may be used toaccurately and effectively bond two elements together.

BACKGROUND OF THE INVENTION

Friction welding is a well-known process in which two components, movingrelative to each other, are brought into contact under pressure andbonded at their interface. The motion at the weld interface may berotational or non-rotational. Non-rotational motion includes linear,elliptical or vibratory motion. Friction welding by rotational motiontypically requires at least one of the components be circular in crosssection. However, friction welding by non-rotational motion has receivedattention as a means of bonding components, where the weld interface ofboth parts is non-circular.

In non-rotational friction welding, one component is oscillated relativeto the other component while a forge force is applied normal to thedirection of motion. The forge force moves the components into contact,and with metal components the friction between the components generatesheat and plasticizes them. Once the motion stops, the metal solidifies,thus bonding the components. This relative simplicity of the process, ascompared to other welding processes, lends itself to methodologies thatpermit tight control of the weld process. Rigid process control mayeliminate the necessity of post-weld inspection of the components. Weldparameters such as frequency and amplitude of oscillation, axialdisplacement, and normal force can be precisely monitored and controlledto produce consistent and repeatable welds.

For plastic components, the friction weld process is typically performedat high frequencies and low forge forces. An example of a process forfriction welding thermoplastic components is disclosed in U.S. Pat. No.4,377,428, issued to Toth and entitled “Method of Friction Welding”.

However, for metal components, the conditions required for frictionwelding are much more stringent. In addition, there are large forcesassociated with friction welding metal components. Typically, for metalcomponents the oscillation frequencies are less than/about 100 Hz,depending on the part size and shape, and the forge forces are greaterthan 5000 lbs. force. A welder having substantial structure is needed towithstand the larger forces associated with friction welding of metalcomponents. Due to the size of such structures, interference between theoscillation frequency and the resonant frequency of the welder is aconcern. In addition, repeatability of the process is necessary forprocess control. Repeatability requires the final position of thecomponents, when welded, to be accurate and predictable.

The actuation system used to generate the oscillating motion must beable to provide a consistent frequency and amplitude and be able tolocate the oscillated component in the proper position for forging. Onetype of actuation system is a mechanically driven system such as thatdisclosed in U.S. Pat. No. 5,148,957, issued to Searle and entitled“Friction Welding”. In this type of actuation system, cams and jointsare used to provide the reciprocating motion. A drawback to mechanicallydriven actuation systems is the wear, which occurs in the systemcomponents. As the system is used, the cams, joints, and bearings willwear which will result in deviations that have to be accounted for, toensure accuracy and repeatability of the process. Eventually the wearwill require replacement of worn parts, which introduces an additionaldeviation to be accounted for. The actuation system will requirere-calibration frequently to account for all the deviations. Anotherexample of a mechanically driven actuation system is disclosed in U.S.Pat. No. 4,858,815, issued to Roberts et al and entitled “FrictionWelder Mechanism”.

Another type of actuation system is a servo-hydraulically controlledactuation system, such as that disclosed in U.S. Pat. No. 4,844,320,issued to Stokes et al and entitled “Control System and Method forVibration Welding”. One limitation to known types of servo-hydraulics isthe interference between the oscillating frequency and the naturalfrequency of the hydraulic column. To generate low frequencies (<100 Hz)and the forge forces needed to move metal components subject to a normalforce, the hydraulic columns needed are typically large enough to havenatural frequencies of the same order of magnitude as the oscillatingfrequency.

A particularly useful application for which friction welding is usefulis in fabricating integrally bladed rotors for gas turbine engines. Anexample of this type of application is disclosed in U.S. Pat. No.5,035,411, issued to Daines et al and entitled “Friction BondingApparatus”. An integrally bladed rotor is a rotor assembly wherein therotor blades are bonded, typically by welding, directly to the rotordisk at spaced intervals about the circumference of the disk. Sincethere are numerous rotor blades bonded to each disk, the bonding processmust be accurately repeatable. In this way individually manufacturedcomponents each with selected properties may be joined. Each bondedblade must be accurately positioned within tight tolerances required foraerospace applications. An improved friction welder and method aresought for friction welding large scale, complex shapes formed fromvarious metallic materials.

DISCLOSURE OF THE INVENTION

The present invention is predicated in part upon the recognition thatnon-planar forces, relative to the plane of the forge pressure, causedeviations in the location of the parts being bonded. The deviationdegrades the accurate repeatability of the welding process.

According to the present invention, a friction welder for joining a pairof elements includes a forge assembly having a table defining a platformfor disposing one of the elements thereon and wherein, during theapplication of forge pressure between the elements, non-planar forces inthe platform are minimized. Forge pressure is generated between theelements by a forge link disposed on one side of the platform andreacted by a reaction link disposed on the opposite side of theplatform. The two links are equidistant from the plane of the platformand connected by a crank that is also pivotally connected to the table.

A principle feature of the present invention is the table having areaction link disposed opposite of the forge link. The advantageproduced thereby is the accuracy of the welded position between the twoelements as a result of the minimized non-planar forces in the platform.Minimizing or eliminating non-planar forces in the platform results inminimizing or eliminating deflections and deviations in the relativepositions of the elements being welded. Another advantage is theaccurate repeatability of the process as a result of the control overdeflections and deviations in relative position.

According to another embodiment of the present invention, a method offriction welding a pair of elements includes the step of balancing themoments in the table such that non-planar forces in the platform areminimized. In a specific embodiment, the method includes the steps ofplacing the forge link in a bent position such that the elements may bepositioned in the welder and placing the forge link in the forgeposition such that forge force may be applied to the elements. The stepof balancing the moments and deflections in the table prior toreciprocating the elements improves the accuracy and repeatability ofthe weld process.

According to a further embodiment, the forge link includes a first end,a second end, both of which are disposed on a forge axis, and a pivotingjoint therebetween. The pivoting joint permits the forge link to beflexed such that the table may be moved away from the point ofengagement between the two elements.

The feature of the forge link having the pivoting joint results in theadvantage of ease of assembly of the elements into the friction welder.The pivoting joint permits the table to move away from the point ofengagement to thereby provide access to the tooling and gripper.

According to a specific embodiment of the present invention, thefriction welder includes a frame having a base, a pair of verticallyextending trusses interconnected at one end and to the base at theopposite end, and a diagonal truss extending between the verticaltrusses and the base. A reciprocal motion assembly is disposed on thediagonal truss. The forge link extends between the diagonal truss andthe crank.

A further feature of the present invention is the capability to use aservo hydraulic control system used in the reciprocating motionassembly. The advantage is the improved control of the reciprocal motionassembly for reciprocating frequencies of less than 100 Hz. Thestiffness of the frame and forge assembly and the minimal length of thehydraulic column within the servo hydraulic control of the reciprocatingmotion assembly results in a natural frequency for the structure servohydraulic control in excess of the reciprocating frequencies required.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are perspective views of a friction welder with anindexing turret removed for clarity.

FIG. 3 is a left side view of the friction welder in FIG. 1, in a loadedoperating mode with the indexing turret removed for clarity.

FIG. 4 is a front view of the friction welder

FIG. 5 is a left view of a forge assembly of the friction welder in aforge loaded position.

FIG. 6 is a left side view of the forge assembly of the friction welderin a forge unloaded position.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, the friction welder 20 is an apparatus for frictionwelding a first element 21 to a second element 22. An indexing turret(base tool) (not shown) which in operation would hold the second element22 in the illustrated position has been removed for clarity. In theillustrated application, the first element 21 is a rotor blade, orairfoil and the second element 22 is a rotor disk. Once all the rotorblades are welded to the rotor disk an integrally bladed rotor isformed.

The friction welder 20 generally includes a frame 23, a forge assembly24, and a reciprocal motion assembly 26. The frame 23 includes aplurality of struts and trusses. A rectangular base is formed from thehorizontal struts, represented by the struts 33 and 34. The rectangularbase together with vertical first, second, third and fourth trusses 29,30, 31 and 32, respectively, form a pyramid-like configuration. Thefirst and second trusses 29 and 30 connect to the opposite ends of thestrut 33 and connect together at a common junction 35 to form avertically extending triangle with the strut 33. The third truss 31extends vertically from the common junction 35 to the center of thestrut 33. The fourth truss 32 extends diagonally from the commonjunction 35 to the strut 34. The frame further includes four supportlegs 38 one at each corner of the base. The pyramid like frame 24 formedby the configuration of struts and trusses is a strong, rigid supportstructure to accommodate the forces associated with the reciprocalmotion assembly 26 and the forge assembly 24 during the friction weldprocess.

Referring to FIGS. 2 and 3, the forge assembly 24 is supported by theframe 23 and provides a forge force or load along a forge axis Fa. Theforge assembly 24 includes a crank 40, a table link 42, a table 44, aforge link 46, and a reaction link 48 (as best shown in FIG. 4).Referring to FIG. 4, the crank 40 has an upper end 50 and a lower end52. The table link 42, which supports the table 44, has an upper surface54 and a first end 56. The first end 56 of the table link 42 ispivotally connected to the crank 40 between the upper and the lower ends50 and 52 of the crank. A platform axis P is disposed a predetermineddistance D_(p) below the upper surface 54 of the table link 42.

The table 44 has a platform 58 to support an indexing turret (notshown). The table 44 further includes a plurality of bores 59 extendingtherethrough (as shown in FIG. 1). The table is disposed on the tablelink 42 so that the table 44 is in a sliding relationship with thestruts 33 and 34 (as shown in FIG. 1) of frame 23. Referring to FIG. 5,the sliding relationship is accommodated by a plurality of rollerbearings 60. The roller bearings 60 are engaged with first bearingsurfaces 62, which are aligned with a motion axis M_(a), and secondbearing surfaces 64, which are perpendicular to the motion axis M_(a).The motion axis M_(a) extends along the length of the diagonal truss 31.The engagement between the roller bearings 60 and the first and secondbearing surfaces 62 and 64 is adapted to provide support for the mass ofthe second element 22 during sliding of the table 44, and to withstandthe forces generated by the reciprocal motion assembly 26.

Referring again to FIG. 4, the forge link 46 is characterized by a firstend 66 and an opposed second end 68. The forge link 46 further includesa first and second linking pivot 70 and 72, a folding pivot 74, aprimary hydraulic actuator 76, a secondary hydraulic actuator 78, and aload cell 80. The first end 66 of the forge link 46 is pivotally engagedwith the upper end 50 of the crank 40 via the first linking pivot 70.The second end 68 of the forge link 46 is pivotally engaged with thefourth truss 31 via the second linking pivot 72. The folding pivot 74 isdisposed between the first and second linking pivots 70 and 72. Theforge axis F_(a) is defined to extend through the first and second ends66 and 68 of the forge link, parallel to the platform axis P. Both thefirst and second linking pivots 70 and 72 are centered on the forge axisF_(a). The folding pivot 74 is positioned so that the center is offset anominal distance D_(Fa) from the forge axis F_(a).

The primary hydraulic actuator 76 extends between and is connected tothe folding pivot 74 and the load cell 80. The forge force is generatedby the primary hydraulic actuator 76. The primary hydraulic actuator 76is connected in a conventional manner to a primary supply of hydraulicfluid 82 via primary conduit 84 to flow the fluid. Forces generated inthe forge link 46 by the primary hydraulic actuator 76 are sensed by theload cell 80.

The secondary hydraulic actuator 78 is adjacent to the first linkingpivot 70, and generates the movement of the forge link 46 between theloaded and unloaded positions. The secondary hydraulic actuator 78 isconnected in a conventional manner to a secondary supply of hydraulicfluid 86 via a secondary conduit 88 to flow the fluid 86.

The reaction link 48 has a first end 90 and an opposed second end 92.The first end 90 is pivotally engaged with the lower end 52 of the crank40. The second end 92 is pivotally engaged with the table 44. A reactionaxis R extends through the first and second ends 90 and 92 of thereaction link 48. The reaction axis R is parallel to both the forge axisF_(a) and the platform axis P. Further, reaction axis R and the forgeaxis F_(a) are equidistant from the platform axis P. As a result of thisgeometry, moments generated in the upper end 50 of the crank 40 by theforge link 46 are opposed by the moments generated in the lower end 52of the crank 40 by the reaction link 48; thus bending moments in theplatform 58, and in the second element 22 (shown FIG. 3) when the secondelement 22 is mounted on the table 60 are minimized or eliminated.

Now referring to FIGS. 1 and 5, the reciprocal motion assembly 26 isadapted to generate reciprocating motion between the first and secondelements 21 and 22, respectively. The reciprocal motion assembly 26includes a hydraulic actuator assembly 90, a load cell 92, and a slide94. The hydraulic actuator assembly 90 is comprised of a plurality ofhydraulic columns, represented by the hydraulic column 96. Each column96 is connected in a conventional manner to a supply of hydraulic fluid98 via a conduit 100 to flow the fluid. The reciprocal motion assemblyshould be a servo-hydraulic motion actuator with a hydraulic columnnatural frequency greater than the frequency of reciprocation. The slide94 is slidingly engaged with the diagonal truss 32 of the frame 24 by abearing assembly 126 (as shown in FIG. 2). Through the hydraulicactuator assembly 90 the slide 94 is made to move along the motion axisM_(a) in a linear reciprocating motion. The motion axis M_(a) isperpendicular to the forge axis F_(a) The hydraulic actuator assembly isconnected to the load cell 92. A gripper 102 (FIG. 3) is attached to theslide 94, and holds the first element 21, so that when the slide 94 ismoved the first element 21 also moves relative to the second element 22.

Set up of the friction welder will now be discussed. Referring to FIG.6, the friction welder 20 in an unloaded position, where the table 44 isspaced from the diagonal truss 31. The forge link 46 is placed into theunloaded position by actuating the second hydraulic actuator 76 (asshown in FIG. 4). Thus, as the forge link 46 pivots at the folding pivot70 the upper end 50 of the crank moves toward the diagonal truss 34, andconsequently the lower end 52 of the crank moves toward the diagonaltruss 34. Due to the reaction link 48 the table 44 moves away from thediagonal truss 34 along the upper surface 54 of the table link. Thisallows access to the table 44 so that the indexing turret (not shown)can be attached. In the unloaded position, the indexing turret 50 issecured to the table 28 and the second element 22 is secured to theindexing turret 50 in the proper weld position, as described incopending U.S. patent application Ser. No. 09/187,073 entitled “IndexingTurret.” In this position, the first element 21 should be loaded intothe gripper 36 as described in copending U.S. patent application Ser.No. 09/187,511 entitled “Gripper.” Now the second element 22 must bealigned with the first element 21, so that their respective bondingsurfaces (not shown) are aligned along the forge axis F_(a).

Now referring to FIG. 1, the friction welding process may start with theapplication of an initial forge load by the forge assembly 24, and thenactivation of the reciprocal motion assembly 28, or the reciprocalmotion may be initiated prior to application of any forge load. Eitherway, desired forge load and oscillating frequencies may be applied viathe forge assembly 24 and the reciprocating motion assembly 26.

Referring to FIG. 6, the forge load is applied by bringing the forgelink 46 into the forge load position by actuating the first hydraulicactuator 76 (FIG. 4). Activation of the first hydraulic actuator 76urges the upper end 50 of the crank 40 to move away from the diagonaltruss 31. As a result, the lower end 52 moves in the opposite direction,and through the reaction link 48 the table 44 is urged toward the thirdtruss 34. Movement of the table 44 in turn causes the mounted indexturret 50 (not shown) and second element 22 to be urged towards thediagonal truss 34. This further results in the bonding surface of thesecond element 22 being brought into contact with the bonding surface ofthe first element. As the forge assembly 46 continues to move the table44 closer to the diagonal truss 32 the forge load is directed along theforge axis F_(a). The load cell 80 measures the forge load.

The forge link 46 has a forge load position, as shown in FIG. 4, and anunload position, as shown in FIG. 6. As shown in FIG. 5, the forge linkis in the forge load position because the forge link 46 is extendedalong the forge axis F_(a). The forge loads are produced when the forgelink is in the forge load position. To prevent the forge link 46 frombuckling from the forge load position into the unload position duringapplication of forge loads, the folding pivot 74 is centered on alocation, which is offset a nominal distance D_(fp) from the forge axisF_(a). This location 109 is offset in the direction opposite of thelocation where the folding pivot 74 would be in the unloaded position(see FIG. 6). Referring to FIG. 6, in the unload position, the forgelink 46 is pivoted so that the forge link no longer lies along the forgeaxis. This bending is facilitated by the linking pivots 70 and 72 andthe folding pivot 74.

Referring to FIGS. 3 and 5, oscillation of the first element 21 isachieved by activation of the hydraulic columns 96 of the hydraulicactuator assembly 90. This causes the slide 94, gripper 102, and thefirst element 21 to reciprocate along the motion axis M_(a). The loadcell 92 measures and only measures to the friction force of the contactbetween the first and second elements 21 and 22.

The application of the forge load and reciprocating load causes thebonding surfaces of the elements to heat up due to friction whichplasticizes the metal components then the forge load joins them. Uponcompletion of the friction weld, while the friction welder is in theloaded position, the first element 21 is freed from the gripper 102, sothat when the forge assembly 26 is actuated, the table 44 moves and thesecond element 22 moves away from the diagonal truss 31, pulling thefirst element 21 now bonded to the second element 22, out of the gripper102. In order to weld subsequent first elements 21 to the second element22, the second element 22 must be rotationally released, rotated androtationally constrained as discussed above. The friction bondingprocess may be repeated for each bonding position on the second elementas discussed above until completion of the integrally bladed rotor.

Although the invention has been shown and described with respect withexemplary embodiments thereof, it should be understood by those skilledin the art that various changes, omissions, and additions may be madethereto, without departing from the spirit and scope of the invention.

What is claimed is:
 1. An apparatus for friction welding of a firstelement to a second element, the apparatus having a planar axis definedby the direction of relative motion between the two elements duringoperation and a forge axis defined by the direction of forge load duringoperation, the apparatus including: a frame including a base; areciprocal motion assembly adapted to generate reciprocating motionbetween the first element and the second element along the planar axis,the reciprocal motion assembly disposed on the frame; and a forgeassembly including: a table disposed in a sliding relationship to thebase, the table including a platform defining a plane parallel with theforge axis and a base tool for the second element positioned on one endof the table, the base tool adapted to position the second element forengagement with the first element upon sufficient sliding motion of thetable, wherein such engagement defines a point of engagement that lieson the forge axis; a crank pivotally engaged with the end of the tableopposite the base tool, the crank having an upper end and an opposinglower end with the table pivotally engaged therebetween; a forge linkhaving a first end pivotally engaged with the upper end of the crank anda second end pivotally engaged with the frame, the forge link includingmeans to produce a forge load along the forge axis, the first end andsecond end being on the forge axis; a reaction link disposed on theopposite side of the platform relative to the forge link, the reactionlink including the first end pivotally engaged with the lower end of thecrank and the second end pivotally engaged with the table, the first andsecond ends of the reaction link being equal distance from the plane ofthe platform as the first and second ends of the forge link.
 2. Theapparatus according to claim 1, wherein the forge link includes apivoting joint disposed between the first end and the second end, thepivoting joint permitting the forge link to bend such that the base toolmay slide away from the point of engagement to provide access to thesecond element and the base tool.
 3. The apparatus according to claim 2,wherein the pivoting joint has a bent position permitting access to thebase tool and a forge load position permitting application of the forgeload, and wherein in the forge load position the pivoting joint isoffset from the forge axis in a direction opposite the location of thepivoting joint in the bent position.
 4. The apparatus according to claim1, wherein the reciprocating means includes a servo hydraulic motionactuator engaged with the first element and adapted to providereciprocal motion along the planar axis, the motion actuator having ahydraulic column natural frequency substantially different from thefrequency of reciprocation.
 5. The apparatus according to claim 1,wherein the forge load means includes a servo hydraulic forge actuatoradapted to extend the forge link, the forge actuator having a hydrauliccolumn natural frequency substantially different from the frequency ofreciprocation.
 6. The apparatus according to claim 1, wherein the frameincludes a pair of vertically extending trusses interconnected at oneend of each of the pair of trusses and connected to the base at theopposing ends, and a diagonal truss having one end connected to the pairof trusses and the opposite end connected to the base, wherein thereciprocal motion means is disposed on the diagonal truss, and whereinthe second end of the forge link is pivotally engaged with the diagonaltruss.
 7. The apparatus according to claim 1, wherein the first elementis a rotor blade, the second element is a rotor disk, wherein the basetool retains the rotor disk, and wherein the reciprocal motion assemblyincludes a gripper for retaining the rotor blade.